1. Field of the Invention
This invention relates to a chuck which can detect when trouble occurs during working by various cutting edge tools.
2. Description of the Prior Art
Conventional tap work is accomplished by feeding an amount of tap pitch per revolution of a main spindle while causing the tap to bite into a prepared hole thereby working to a predetermined depth.
At this time, a provision is made for the case where a correct amount of pitch per revolution of the tool main spindle cannot be fed. That is, when the tool main spindle has a great feed per revolution, the tap moves to a compression side. Meanwhile, when the tool main spindle has little feed per revolution, the tap moves to a tension side. In this manner, the work is carried out.
Prior to an initial work operation, the tap always waits at a neutral position.
A high load could allow a torque limiter to operate, thereby preventing the tap from being damaged. However, when the torque limiter operates, many vibrations and impacts are generated due to its mechanism. These vibrations and impacts shorten the tap life. Moreover, as the tap is worn and then its life comes closer to the end, it is difficult for the top to bite into the prepared hole. Thus, since the work is carried out by the as compressed tap, a tap depth is reduced.
Moreover, the plucking of a thread would result in defectives.
Then, the tool main spindle is reversely revolved so as to pull out the tap. Thereby, the above-described compressed tap necessarily returns to its original position due to the tension for the subsequent work operation.
According to a working method as described above, the tap, which is shrunk due to an undesirable influence during the work operation, is restored to its original condition by the tension before entering the subsequent work. Thus, the length (overall length) of the tap from one end to the other end is fixed at the time of the initial work operation. It is not therefore possible to visually detect when trouble with the work operation occurs.
Thus, even if the trouble is sensed by an intermediate sampling inspection or the like, many workpieces which have been processed before the trouble is sensed are defective. The rework or the like results in a considerably high product cost and also yields bad productivity.
It is contemplated that an automatic detecting device such as a touch sensor can be used together with the tap. However, only the breakage of the tap is detected. It is impossible to sense that the tap depth is shallow and the plucking of the tap thread causes the defective workpieces.
Moreover, for cutting the workpiece by the use of a cutting edge tool such as a cutter, a drill or a reamer, the tool main spindle rotates and reciprocates the cutting edge tool in a chuck by a predetermined length.
However, the trouble is caused due to the life of the cutting edge tool, a working condition, a working environment or the like. If the cutting work is continued with the trouble caused, the defective workpieces (with a rough cut surface, for example) are produced.
For sensing these defective workpieces, they are discovered sampling detection of the workpieces, or the like, is carried out. Many workpieces which have been worked prior to the detection are defective. The rework or the like causes the product cost to significantly rise and also yields bad productivity.
It can be also contemplated that the automatic detecting device such as the touch sensor is used together with the tap. However, only the breakage of the cutting edge tool or the like is detected. A faulty cut surface or the like cannot be sensed.
An object of this invention is therefore to provide a chuck which can rapidly sense the trouble occurring during the work operation.